- EFF (https://www.eff.org/.well-known/dnt-policy.txt)
- Read the Docs (https://readthedocs.org/.well-known/dnt-policy.txt)
Sites that implement DNT should respond to either /.well-known/dnt-policy.txt or /.well-known/dnt/ or both.
Responding to /.well-known/dnt/ means a site has implemented the W3's Tracking Preference Expression (https://www.w3.org/TR/tracking-dnt/). This doesn't necessarily mean much as there's no agreed standard of what complying with DNT means. However, it typically implies that the site does something different for users with DNT enabled vs. disabled.
Responding to /.well-known/dnt-policy.txt is typically stricter and means a site adhere's to the EFF's guidelines (https://github.com/EFForg/dnt-guide) for DNT. This has rules for how long data is retained, which data can be retained, specifications around anonymizing data, and security precautions.
Disclaimer: I worked on Read the Docs' DNT implementation.